Added double_char.py

Author: Alfredo Miranda

python/string-2/double_char.py

@@ -0,0 +1,8 @@
+# Given a string, return a string where for every char in the original, there 
+# are two chars.
+def double_char(str):
+    str2 = []
+    for c in str:
+        str2.append(2*c)
+        
+    return "".join(str2)